The present invention relates to a measurement system that produces a more precise measurement of the latent radiation that is stored in a radio photoluminescent (RPL) glass which has been irradiated by gamma or similar radiation. The radiation stored in the RPL glass is released in the form of photoluminescence by irradiating the glass with ultraviolet light. The measurement system captures and processes the emitted photoluminescence and displays it.
Measurement systems of the type referred to above are known from German Patent No. 27 44 020. In one known system, a source of ultraviolet light is used to excite the RPL glass to cause it to emit a luminescent radiation the intensity of which is representative of the dosage of gamma or x-ray radiation which is stored in the RPL glass.
Although known radiation measuring systems account for and/or eliminate errors that may result from variations in the light level that is emitted from the source of ultraviolet light, the known systems are nevertheless prone to errors which arise from drifting parameters in light transducers and in integrators that are invariably present in systems of this type. To overcome the above-mentioned disadvantages, Federal Republic of Germany Patent No. 27 45 080 and Federal Republic of Germany laid-open application No. OS 27 45 081 have proposed to include a highly stable reference light source in each of the two light measurement branch circuits that are typically present in a system of the type referred to herein.
Nonetheless, a problem remains. The problem arises from the coupling of an individual reference light source in each measurement branch circuit. There are always minute undetectable variations in the outputs of any two light sources, even highly stable light sources. Negative or positive excursions in the outputs of the reference light sources may not always cancel one another. In fact, these undesirable output excursions associated with the light sources may, at times, reinforce one another, producing significant skewing and worsening of the measurement errors. The magnitude of the errors attributable to the reference light sources can reach values close to 50% of actual measurement values.